title: Macro creatine kinase BB isoenzyme in serum: most likely an antigen-autoantibody complex.
abstract: Nine sera containing an abnormal creatine kinase BB isoenzyme, "macro CK-BB", were examined. Immunoglobulin precipitation after addition of radiolabelled CK-BB suggested that in eight of the sera the enzyme was linked to an immunoglobulin G. Results obtained with papain-digested and with pepsin-digested IgG suggested that the binding of CK-BB occurred in the antigen-binding region (the "Fab-region") of IgG. Each of the two antigen-binding fragments of IgG, obtained by papain-digestion, were CK-BB specific, since they complexed this isoenzyme equally well when excess CK-MM and CK-MB was added. From Scatchard plots the affinity constant for binding of CK-BB to IgG and the BB-binding capacity of four of the sera was calculated. The affinity constant was high and differed little between the sera (range 0.7 x 10(11)-1.6 x 10(11)1/mol). The BB-binding capacity differed widely (range 21-900 microgram of CK-BB per litre of serum), but in each serum it roughly paralleled the activity of the macro CK-BB complex. The results suggest that in eight of the nine sera examined the BB-binding IgG is an antibody with activity directed towards CK-BB.
mesh_terms: D000368:Aged; D000936:Antigen-Antibody Complex; D001323:Autoantibodies; D003402:Creatine Kinase / Q000097:blood* / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007136:Immunoglobulins / Q000302:isolation & purification; D007527:Isoenzymes; D007700:Kinetics; D008875:Middle Aged; D010434:Pepsin A
chemical_list: D000936:Antigen-Antibody Complex; D001323:Autoantibodies; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007136:Immunoglobulins; D007527:Isoenzymes; D003402:Creatine Kinase; D010434:Pepsin A